chore(contract-validator): marketplace integration (#192)

- Add contract-validator to marketplace.json with proper metadata
- Update CLAUDE.md plugin table and commands list
- Validation passes with ./scripts/validate-marketplace.sh

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.claude-plugin/marketplace.json

@@ -181,6 +181,22 @@
       "category": "visualization",
       "tags": ["dash", "plotly", "mantine", "charts", "dashboards", "theming", "dmc"],
       "license": "MIT"
+    },
+    {
+      "name": "contract-validator",
+      "version": "1.0.0",
+      "description": "Cross-plugin compatibility validation and Claude.md agent verification",
+      "source": "./plugins/contract-validator",
+      "author": {
+        "name": "Leo Miranda",
+        "email": "leobmiranda@gmail.com"
+      },
+      "homepage": "https://gitea.hotserv.cloud/personal-projects/leo-claude-mktplace/src/branch/main/plugins/contract-validator/README.md",
+      "repository": "https://gitea.hotserv.cloud/personal-projects/leo-claude-mktplace.git",
+      "mcpServers": ["./.mcp.json"],
+      "category": "development",
+      "tags": ["validation", "contracts", "compatibility", "agents", "interfaces", "cross-plugin"],
+      "license": "MIT"
     }
   ]
 }